Stringent emissions regulations such as those imposed by U.S. and European regulatory officials have progressively reduced the amount of diesel particulate matter (DPM) and other gaseous constituents such as NOx allowed in the exhaust gases of diesel engines. The emissions levels proposed by the US07 and Euro 5 regulations are so low that they can be currently met only with the use of exhaust aftertreatment devices. A diesel particulate filtration device (DPF) is an example of a device which may be used to comply with particulate emissions levels in a diesel engine. A diesel oxidation catalyst (DOC) may be used to convert hydrocarbons and carbon monoxide to carbon dioxide and water vapor. A DOC can also be used in conjunction with a DPF device to raise the temperature of the DPF for regeneration, that is, removing collected carbon particulate matter. Lean NOx absorbers and Selective Catalytic Reduction (SCR) devices are examples of systems used for reducing NOx in the exhaust gases.
It is necessary at times to inject substances into the engine exhaust to facilitate or initiate a function of an aftertreatment device. With diesel particulate filters, for example, it is sometimes necessary to raise the temperature of the exhaust gas to oxidize the collected particulate matter in the filter for removal, a process known as regeneration. Regeneration may be done by methods including injecting hydrocarbons into the exhaust flow.
One method is to inject a hydrocarbon into the exhaust gas and use a catalytic device that elevates exhaust gas temperature by catalytically oxidizing the injected hydrocarbon. FIG. 1 shows schematically an internal combustion engine 5 with an exhaust system layout including a stack pipe or tailpipe 10, which disperses the exhaust gas to the environment, and exhaust aftertreatment devices, in this illustration, a diesel particulate filter 12, and a diesel oxidation catalyst 14. FIG. 1 shows an injection device 16 mounted on the exhaust downstream of the exhaust side of the turbine 18 of a turbocompressor. Hydrocarbon injected by the injector 16 mixes with the exhaust gas and is oxidized when it comes into contact with the catalyst, releasing heat energy. The heated gases enter the diesel particulate filter and cause much of the accumulated particulate matter to oxidize.
A problem with an injector mounted on an exhaust conduit is that particulate matter in the exhaust gases, which prior to the aftertreatment devices has not been filtered out, tends to collect on and foul the injector nozzle. This fouling or accumulated carbon deposits, can block the nozzle outlet or disrupt the flow pattern of the nozzle. A fouled nozzle requires cleaning, which results in vehicle downtime and maintenance costs.
According to the invention, fouling can be prevented or diminished by creating a positive flow of air or another clean gas around the nozzle to inhibit the flow of exhaust gases from reaching the nozzle.
The invention proposes a device that can be mounted between the injector and the exhaust conduit that guides a flow of air or another clean gas to the nozzle. In its simplest form, a device in accordance with the invention includes a plate-shaped member having a bore to provide communication between the nozzle of the injector and an opening in the exhaust conduit. The plate-shaped member includes an inlet to receive air from an air source, and has defined therein a passageway to guide the received air to at least one outlet. The at least one outlet directs the air into a space around the nozzle, the space being defined at least in part by the bore. The device directs air or another gas into a cavity in which a hydraulic flow nozzle is disposed to maintain a constant or nearly constant outward flow of gas so as to prevent the ingress of particles, materials or other contaminants that could be in the environment outside of the cavity (that is, the exhaust conduit 20).
Alternatively, rather than being formed as a separate member, the anti-fouling device may be integrated into an injector outside the nozzle or integrated into the wall of an exhaust conduit 20.
According to the invention, the at least one outlet may be formed in the member in a position so that air exiting the outlet surrounds the injector nozzle, either directly of indirectly. The at last one outlet may be formed in a wall defining the bore to direct a flow of air at the nozzle.
The at least one outlet may be formed as a hole. Alternatively, the at least one outlet may be formed as an air jet or nozzle shaped opening. According to another alternative, the at least one outlet may be formed as a slot in the wall defining the bore. Other outlet shapes may be used.
According to one embodiment, the bore may be shaped to define a cavity to receive the nozzle, the cavity defining the space around the nozzle and opening to an aperture to allow the injection of hydrocarbon or other substance from the injector into the exhaust pipe.
According to another embodiment, the plate member includes a recess area surrounding the bore on a side that mates with the injector, which defines an annular gap around the injector nozzle. The passageway guides air to the recess area and annular gap, which causes the air to form a ring-shaped curtain around the nozzle. The passageway may be formed in part by a space between the injector body and a top surface of the plate.
According to the invention, an anti-fouling device delivers air or another gas at a pressure higher than the pressure of exhaust gases in the exhaust conduit to hinder exhaust gas from contacting the injector nozzle.
According to the invention, an anti-fouling device delivers air or another gas to a vicinity of an injector nozzle with sufficient velocity to prevent or hinder exhaust gas from contacting the nozzle.